In view of the importance of resistance to liquid leakage, elastic bodies such as rubber are used in parts which slide while maintaining a seal, e.g., a gasket which is integrated with a plunger of a syringe and forms a seal between the plunger and the barrel. Unfortunately, such elastic bodies have a slight problem with the sliding properties (see Patent Literature 1). To address this problem, a sliding property improving agent, for example silicone oil, is applied to the sliding surface; however, a concern has been raised over the potential adverse effects of silicone oil on recently marketed bio-preparations. On the other hand, gaskets not coated with a sliding property improving agent have poor sliding properties and therefore do not allow plungers to be smoothly pushed but cause them to pulsate during administration, resulting in problems such as inaccurate injection amounts and infliction of pain on patients.
To satisfy the conflicting requirements, that is, resistance to liquid leakage and sliding properties, a method of coating surfaces with a self-lubricating PTFE film has been proposed (see Patent Literature 2). Unfortunately, such PTFE films are generally expensive and increase the production cost of processed products, limiting the range of application of the method. Also, products coated with PTFE films might not be reliable when they are used in applications where sliding or the like is repeated and durability is therefore required. Furthermore, since PTFE is vulnerable to radiation, PTFE-coated products unfortunately cannot be sterilized by radiation.